STEAM-WATER CAPILLARY PRESSURE IN GEOTHERMAL SYSTEMS

Abstract

Steam-water capillary pressure has a significant effect on water injection into and production from geothermal reservoirs. The mass transfer between steam and water phases makes it very difficult to measure steam-water capillary pressure using routine methods such as the semipermeable porous plate method and centrifuge method. Due to the difficulties in measuring steam-water capillary pressure, very few steam-water capillary pressure data are available. We used a steady-state flow method to measure steam-water capillary pressures using an X-ray CT technique to monitor and measure the saturation and distribution of water in the core sample. The drainage steam-water capillary pressure was calculated using a formula derived from the Kelvin equation after measuring the pressures and temperatures of the water phase. The steam-water capillary pressure of the Berea sandstone sample was about 0.07 MPa (10.4 psi) at a water saturation of around 30% and a temperature of about 120oC. The steam-water capillary pressure of the Berea sandstone sample was scaled up for a rock from The Geysers field using the experimental data of steady-state flow and the results obtained were consistent with those measured by Persoff and Hulen (1996) using an adsorption method. A mathematical model to calculate steam-water capillary pressure of geothermal rocks has been developed for application in geothermal reservoir engineering and numerical simulation..